P

prkaye

Well Known Member
I was just looking at my newly completed elevator, and saw that the white powder coating was peeling off my elevator horn!!!! Has anyone else ever experienced this with PC parts?

Replacing the horn will not be practical, as the elevator is completed. I sprayed some self-etch primer over the bare steel... will this suffice for now? When it comes time to paint the aircraft, will it suffice to just prime and paint these?
 
Regarding steel parts powder coated - tick, tick, tick. Powder coating looks nice, but it is a terrible corrosion preventative. I'm sure many will disagree, but if I were building another plane, I'd get the parts in the raw.
 
Same thing happened to my horns...the coating peeled away at the edges...very frustrating. I cleaned up the edges as much as possible, and recoated them with a "touch-up" powder coat paint sold by Vans. Don't know it this is the best approach or not???
 
I have also questioned the quality of the powder coated pieces in the kit. My small aileron pushrods were terrible. I sanded, primed and they will be painted with the aircraft. I also chipped an edge on the control column yoke. I have a 10 year old tube and rag powder coated float plane that had high quality powder coating and still looks good, although I used tube seal oil inside this airframe. Vans sells a touch up kit for powder coat but I haven't tried it. If you have a large area it will need to be sanded cleaned and painted.
 
PC's sealing integrity/durability, like paint, it comes down to the prep and bonding.

To me, the overriding benefit of the PC is it's durability. It may be a *slightly* less capable sealing membrane, but I believe it's generally more durable than paint coatings.

Sounds like Van's PC provider may have a QC issue. To answer the original question, depending on the colors, I would just clean and paint the damaged part with the aircraft coating system.
 
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Low Pass said:
Sounds like Van's PC provider may have a QC issue.
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It's not Vans provider that has the QC issue....it's Vans.

Vans send their components out to multiple powdercoaters without any specification whatever. They buy on price. I know this to be a fact because I've asked them for a copy of their spec sheet on the powdercoating and they have admitted they don't have one.

All Vans powdercoated components should be zinc electroplated before being powdercoated to an appropriate written specification. I was going to have all of my powdercoated components stripped down and done this way but it was logistically impossible with a slo-build coming in multiple deliveries. The parts that will prove to be a nightmare for anyone in a marginally corrosive environment (including me) will be those powdercoated components that are rivetted into place and cannot be readily accessed again (eg most of the empennage fittings).
 
Hit and miss

My 6A kit from 6 years ago had some iffy power coating on many components. My 10 kit has awesome powder coating especially on the engine mount where I had to remove it to weld new tubes on- like granite! Great if you are not planning to remove it. I have to file it off, sanding is virtually useless.
 
Captain Avgas said:
It's not Vans provider that has the QC issue....it's Vans.

Vans send their components out to multiple powdercoaters without any specification whatever. They buy on price. I know this to be a fact because I've asked them for a copy of their spec sheet on the powdercoating and they have admitted they don't have one.

All Vans powdercoated components should be zinc electroplated before being powdercoated to an appropriate written specification. I was going to have all of my powdercoated components stripped down and done this way but it was logistically impossible with a slo-build coming in multiple deliveries. The parts that will prove to be a nightmare for anyone in a marginally corrosive environment (including me) will be those powdercoated components that are rivetted into place and cannot be readily accessed again (eg most of the empennage fittings).
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OK. Van's has a QC problem.

What do you mean, "they buy on price"? With or without a spec, I would hope "they buy on price".

As for your PC'd parts. Why don't you strip them down one-by-one as they arrive and paint them if you're concerned?
 
Typically in a manufacturing situation you should buy on specification followed by price, availibility, etc. as they apply to your needs. Price is always very important but without specifications you don't know for sure what you will get.

Just my $.02 worth. :)
 
Sometimes when reading threads and I come across statements like "...All Vans powdercoated components should be zinc electroplated before being powdercoated to an appropriate written specification...." it makes me wonder if one should ask:

"....how much do you want to pay for this kit? :confused: "

The product is such a great value which, through Van's desire to share the joy of flight with as many folks as possible by offering reasonable quality at conservative pricing, enables average folks with average incomes to make superlative aircraft for their personal use.

Can the kit be improved? Yes!, but what it will never do is to satisfy everyone.
 
Improvements Don't always mean more cost ...

Power Coating Comments from this thread:

"I was just looking at my newly completed elevator, and saw that the white powder coating was peeling off my elevator horn!!!! "

"Same thing happened to my horns...the coating peeled away at the edges...very frustrating. "

"I have also questioned the quality of the powder coated pieces in the kit. My small aileron pushrods were terrible. "

"My 6A kit from 6 years ago had some iffy power coating on many components."

"My 10 kit has awesome powder coating especially on the engine mount where I had to remove it to weld new tubes on- like granite!"

Being a manufacturing engineer for the past 25 years, I've learned that decreasing variation and improving quality often can be achieved at no cost - its just a matter of understanding and eliminating sources of variation within your current process. (no need to do added cost processing like zinc electroplating if you can achieve "terrible" and "granite" results within the same basic process).

I'm still in the dreaming phase of building an RV, but knowing I've gotten the "terrible" powder coat while someone else got the "granite" one at the same cost would be frustrating and just screams of process variation.

The supplier has no incentive to explore this unless Van's actually says something about it to them. Van's is more likely to say something about it if builders say something about it to them.

I've learned a lot from this forum, and appreciate the opportunity to pipe in once in a while.

Thank you
Tim
 
Incidentally, if you're really worried about it, just do what I would do next time around. Just ask for the parts with no powder coat. It's a pretty sure bet that SOMEONE in your area is building a tube and fabric plane and probably has a sand blaster lying around you can use.

In my case, the powder coating was acceptable mostly (layed on a bit thick at times, but not too bad) but the color scheme I had in mind would have looked silly with all this white stuff hanging all over the place. Much easier for me to just paint it "right" the first time then to strip it and repaint it.

To put it in perspective, though, of the thousands and thousands of powder coated parts flying in 4500+ airplanes, I haven't read one post anywhere about worrisome corrosion on any of Van's steel. So it's not perfect but it's not THAT bad I guess :)
 
No QC

JohnR said:
Typically in a manufacturing situation you should buy on specification followed by price, availibility, etc. as they apply to your needs. Price is always very important but without specifications you don't know for sure what you will get.

Just my $.02 worth. :)
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Absolutely 100% correct. Price is always important but ONLY if all subcontractors are quoting on the same thing...otherwise it is meaningless.

The powdercoating industry in particular is full of sharks. If you don't provide a written specification you will always find some-one who will do a crappier job at a cheaper price. They just cut more corners, such as: inadequate or no degreasing, inadequate or no passivation, inferior powders, insufficient oven temperatures/times (to cut overheads), excessive oven temperatures/times (insufficient staff and/or lack of monitoring). It just goes on and on.

For all of the builders who are advocating the use of Sikaflex for bonding on their canopies I recommend they think carefully about what might be the really weak link...the bond of the powdercoat to the steel (and not just today but down the track when there's corrosive undercreep of the powdercoat due to inferior pretreatment).
 
Captain Avgas said:
For all of the builders who are advocating the use of Sikaflex for bonding on their canopies I recommend they think carefully about what might be the really weak link...the bond of the powdercoat to the steel (and not just today but down the track when there's corrosive undercreep of the powdercoat due to inferior pretreatment).
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I thought those that were using sikaflex sanded off the powdercoat before bonding the canopy to the frame ... ?

T.
 
Captain Avgas said:
Absolutely 100% correct. Price is always important but ONLY if all subcontractors are quoting on the same thing...otherwise it is meaningless.

The powdercoating industry in particular is full of sharks. If you don't provide a written specification you will always find some-one who will do a crappier job at a cheaper price. They just cut more corners, such as: inadequate or no degreasing, inadequate or no passivation, inferior powders, insufficient oven temperatures/times (to cut overheads), excessive oven temperatures/times (insufficient staff and/or lack of monitoring). It just goes on and on.

For all of the builders who are advocating the use of Sikaflex for bonding on their canopies I recommend they think carefully about what might be the really weak link...the bond of the powdercoat to the steel (and not just today but down the track when there's corrosive undercreep of the powdercoat due to inferior pretreatment).
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Tell us (me) more about this zinc coating before PC. Is this for adhesion or sacraficial corrosion coating? What role does anchor pattern play in PC bonding?

The points made about application and prep specifications for PC systems are good, but are equally applicable to other coating systems. And then it can be said that even the tightest spec may be useless without proper QA from the owner or end user.

Good info.
 
Low Pass said:
Tell us (me) more about this zinc coating before PC. Is this for adhesion or sacraficial corrosion coating? What role does anchor pattern play in PC bonding?

The points made about application and prep specifications for PC systems are good, but are equally applicable to other coating systems. And then it can be said that even the tightest spec may be useless without proper QA from the owner or end user.

Good info.
Click to expand...

Firstly I doubt that many of the builders who are opting for the Sikaflex canopy technique remove the powdercoating...none of the ones that I have personally seen have removed it...they just apply the Sikaflex to the existing powdercoat...and hope for the best.

In response to your question above. The problem with powdercoat is that it is purely a barrier protection. Once the barrier is broken (scratch, crack,etc) the steel underneath can oxidise (rust) and the oxidisation runs underneath the powdercoat destroying the adhesion. That's why powdercoaters normally apply a passivating pretreatment (typically iron or zinc phosphate). Iron and zinc phosphates are a non-metallic coating that inhibits corrosion undercreep and increases the adhesion and durability of the powdercoat.

However iron and zinc phosphates are a relatively poor passivation. If you take a piece of steel that is iron or zinc phosphated and put it in a salt spray cabinet it will rust within a very short time.

Zinc electroplating on the other hand provides far superior corrosion protection of the steel and therefore is significantly better at preventing corrosion undercreep.
 
My engine mount

Interestingly enough, I had my engine mount powder coated in Los Angeles near all of the aerospace companies.

The shop said they would prime it before powder coating it, and when asked what the primer was, they said it was military primer - turned out to be the MIL-P-23377 primer mentioned in "primer wars...

Since they had large drying ovens (one car garage size with open gas flames at the bottom), it didn't take long for the primer to dry/cure.... :)

Since this primer is strontium chromate, I guess it provides the sacrificial coating mentioned in the previous post.

However, I hadn't heard of priming before powder coating before, perhaps it's an aerospace thing?

gil in Tucson
 
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